def s()
  n = gets.to_i
  a = gets
  if a.count(" ") > 0
    return "assert"
  end
  a = a.to_i
  b, c = gets.to_i, gets.to_i
  s = [a+b,b+c,c+a].sort
  if s[0] == s[1] 
    return s[2]
  elsif s[1] == s[2]
    return s[0]
  end
  return s[1]
end

puts s()